1. Field of the Invention
The present invention relates to a capacitor and a method for manufacturing the same. More particularly, the present invention relates to an electric double layer capacitor where the specific capacitance is improved by using an additive in the preparation of electrodes for the capacitor and a method for manufacturing the same.
2. Description of the Prior Art
An electric double layer capacitor (hereinafter referred to as an “EDLC”) means a capacitor using an electric double layer that are formed at interfaces between the electrode and electrolyte. As for the structure of an EDLC, it is composed of a pair of polarized electrodes with a separator located therebetween, an electrolyte, a current collector and a case for housing all of them. Activated carbon and carbon alloys (carbon/metal composites) are widely used as materials for EDLC electrodes. Recently, polyacenic semiconductor (PAS), an intermediate between electroconductive polymers and carbon, etc., have been developed and used as a new type of carbon electrode.
Generally, activated carbon, suitable for use as polarized electrodes materials of EDLC, is made from a vegetable material, such as coconut palm shell and cellulose etc., carboniferous or petrolic pitch or cokes, or a thermosetting resin, such as phenol resin, etc. and polyacrylonitrile (PAN), etc. Various attempts have recently been made to modify activated carbon with the aim of improving the specific capacitance of EDLC, which is used as material for polarized electrodes of EDLC.
For example, Japanese Pat. Laid-Open Publication No. 7-220985 discloses the formation of meso pores and improvement of diameter of meso pores. Japanese Pat. Laid-Open Publication Nos. 7-249551 and 9-213589 describe EDLC's the capacitance of which is increased through the modification of materials for activated carbon.
Particularly, Japanese Pat. Laid-Open Publication No. 7-220985 teaches that activated carbon is effective as electrode materials for increasing the capacitance of EDLC in aqueous electrolytes when it has micro slit or oval pores a width and length 1.5 to 3.0 times larger than the diameter of water molecules, and is effective as electrode materials for increasing the capacitance of EDLC in organic electrolytes when the micro pores are 0.2 nm larger than the diameter of the dissolved ions in the electrolyte.
Further, in Japanese Pat. Laid-Open Publication No. 7-249551, polyvinylidenechloride (hereinafter referred to as “PVDC”) is thermally treated at 800˜1,000° C. in a non-oxidative atmosphere to afford a carbon material, having meso pores, suitable for use as EDLC electrodes.
Meanwhile, in order to provide an electrode with a high-specific capacity, Japanese Pat. Laid-Open Publication No. 9-213589 employs an activated carbon material containing a polymer of vinylidene chloride or a copolymer of vinylidene chloride with other monomers in an amount from 10 to 100 wt %, and preferably in an amount from 80 to 97 wt % as PVDC resin.
Most such conventional methods for improving EDLC in electrostatic capacitance are based on the addition of additives to activated carbon.